In the last century reconstructive and cosmetic surgery has become a common practice. Specifically cosmetic breast surgery has been developed to allow reconstruction of a woman's breast that was affected by procedures such as mastectomy. Cosmetic breast surgery has also become available to amend the appearance of a woman's breast, for example by adding an implant to increase the size of the breast, to correct asymmetries, change shape and fix deformities.
For reconstructive and cosmetic surgery, the implant is required to be able to provide a specific three-dimensional shape and maintain the shape for many years, preferably for the lifetime of the woman (or man, depending upon the type of surgery) in which the implant is installed to prevent the need for additional invasive surgery. The implant is also required to have a specific feel, preferably imitating the feel of human tissue, such as the feel of a real breast. The implant also needs to be bio-durable such that it is not ruined by interaction with the human body; and it needs to be bio-compatible so that the patient's health is not detrimentally affected by the implant even under extreme circumstances: for example the implant is required to be non toxic in case of leakage from the implant.
The standard implants used today for breast implant surgery for example comprise an outer shell typically formed from vulcanized silicone rubber (elastomer) which can be single or multi layered, smooth or textured, barrier-coated, or covered with polyurethane foam; and an inner content typically formed from silicone gel or inflated during surgery with saline. An average implant may weigh between 50 to 1000 grams, or even more. The specific weight of the commonly used filling materials is generally between 0.95 to 1.15 grams per cubic centimeter volume, similar to the specific weight of the natural breast tissue.
Nevertheless, natural breast tissue is a live tissue undergoing a common natural lifecycle just as any other tissue within the body, while a breast implant is “dead weight” added to the breast tissue. Both natural breast tissue and breast implants are subjected to forces of gravity. The most common response of both natural breast tissue and breast implants to gravity is sagging over time. The rate of sagging is enhanced in implants as implants are a “dead weight”.
Over time breast implants are known to cause many problems, mostly related to the weight of the implant, for example: ptosis (i.e. sagging and deformity), breast tissue atrophy, prominence of the implant through breast tissue, back pain, and striae of the skin. Thus, the weight of the implant is an important factor in post-surgical comfort and appearance.
Traditionally, the silicone gels used as filling materials had silicone oils featuring small liquid molecules such as linear or cyclic silicones, silicone oligomers and low molecular weight silicone polymer chains in them that leached out through the shell over time. Current implants involve the use of a shell with barrier layers to achieve very low permeability of those liquid moieties. In addition, the silicone gel used in breast implants is considered a “cohesive” gel. The cohesiveness ensures that the filling material does not easily flow and spread out into the body, in case of rupture of the shell; it also significantly reduces silicone oil diffusion through the shell.
An additional characteristic to be considered in selection of the filling material is the resilience, elasticity and pliability of the implant, which provides it with a specific feeling when being sensed. Generally it is desirable to provide an implant which provides a specific shape and mimics the feel of real human tissue at the position of the implant. It is important that the implant maintain its form and feel for extended periods, to prevent the need for additional surgery.
US Patent Application Publication No. 2004/0153151 to Gonzales dated Aug. 5, 2004 describes a breast prosthesis from silicone that is formed as a trabecular body or micro-cell body in order to obtain a prosthesis of lower density.
U.S. Pat. No. 4,380,569 to Shaw dated Apr. 19, 1983 describes a reduced weight breast prosthesis which is worn external to the human body or implanted into the human body. The breast prosthesis is comprised from a mixture of a silicone gel with glass micro-spheres.
U.S. Pat. No. 5,902,335 to Snyder, Jr. dated May 11, 1999 describes a reduced weight breast prosthesis which is worn external to the human body. Snyder states that the use of glass micro-spheres as described by Shaw results in a stiff product that does not mimic the human breast as well as silicone gel alone. Snyder describes a breast prosthesis having two sections. A first outer section filled with silicone gel that mimics the human breast and a second inner section of reduced weight to reduce the weight of the prosthesis.
U.S. Pat. No. 5,658,330, to Carlisle et al. dated Aug. 19, 1997 describes a molded silicone foam implant and method for making it.